Turbocharger and adjustable blade therefor

ABSTRACT

An adjustable blade for turbocharger applications, particularly in diesel engines, is described, which consists of an iron-based alloy with an austenitic basic structure with dendritic carbide precipitations.

The invention relates to an adjustable blade for turbocharger applications, particularly in a diesel engine, according to the preamble of claim 1, and also to an exhaust gas turbocharger with an adjustable blade, according to the preamble of claim 5.

Exhaust gas turbochargers are systems for increasing the power of piston engines. In an exhaust gas turbocharger, the energy of the exhaust gases is utilized for increasing the power. The power increase results from a rise in the mixture throughput per working stroke.

A turbocharger consists essentially of an exhaust gas turbine with a shaft and compressor, the compressor arranged in the intake tract of the engine being connected to the shaft, and the blade wheels located in the casing of the exhaust gas turbine and in the compressor rotating. In a turbocharger with variable turbine geometry, adjustable blades are additionally mounted rotatably in a blade bearing ring and are moved by means of an adjustment ring arranged in the turbine casing of the turbocharger.

The adjustable blades, as they are known, have to satisfy extremely stringent material requirements. The material forming the adjustable blades must be heat-resistant, that is to say still show sufficient strength even at very high temperatures of up to about 900° C. Furthermore, the material must have high wear resistance and also corresponding oxidation resistance, so that the corrosion or wear of the material is reduced, and, consequently, the resistance of the material under the extreme working conditions is still ensured. Moreover, material is to be resistant to erosive attacks. These physical properties of the material are also to be reflected in the component, that is to say the adjustable blade.

Heat-resistant materials for exhaust gas turbochargers or their individual components are known from EP 1 396 620 A1. What is considered suitable here is a material which has a specific composition, the surface of the components being capable of being coated with a chrome carbide layer, and the material having a low fraction of small, non-metallic inclusions. A heat resistance of the turbocharger or of its individual components of up to 700° C. or more is thereby to be achieved.

By contrast, the object of the present invention is to provide an adjustable blade according to the preamble of claim 1 and a turbocharger according to the preamble of claim 5, which have improved temperature and oxidation resistance, and erosion resistance under extreme temperatures, and also a corresponding wet corrosion resistance, which are distinguished by optimal tribological properties and, moreover, which exhibit a reduced susceptibility to wear.

The object is achieved by means of the features of claim 1 and of claim 5.

Owing to the design according to the invention of an adjustable blade or an exhaust gas turbocharger comprising just such adjustable blades, a better temperature resistance of the component is achieved. This is also increased by a multiple by means of the dendritic carbide precipitations contained in the iron-based alloy, that is to say a carbide microstructure contained in the iron-based alloy and having fine ramifications and, furthermore, dispersions of nitrogen in the form of nitride structures. An adjustable blade or an exhaust gas turbocharger is thus provided which contains the adjustable blades according to the invention, which has optimal temperature resistance in the range of up to 900° C., furthermore is highly heat-resistant, has high wear, erosion and corrosion resistance and, moreover, is also distinguished by very good sliding properties, along with reduced oxidizability.

Furthermore, the adjustable blade according to the invention remains dimensionally stable and therefore highly planar, that is to say is distinguished by a high strength of the material forming it.

Without being involved in theory, it is presumed that carbide precipitations in the form of dendrites increase the stability of the iron-based alloy in that they form in the microstructure of the material fine ramifications which perform a supporting action, so that the strength of the material and therefore the strength of the adjustable blade according to the invention are markedly increased on account of their unique structure. The dispersions of the element nitrogen in the form of nitride structures in this case additionally increase the wear performance and corrosion resistance.

The material forming the adjustable blade according to the invention or the adjustable blade, moreover, exhibits optimal resistance to intercrystalline corrosion.

The maximum wear rate of the adjustable blade according to the invention in this case amounts to less than 0.08 mm for a bearing load of 10 to about 18 N/mm², a sliding speed of 0.0025 m/s, a component temperature of about 500 to 900° C., a surface roughness Rz of 6.3, a test duration of 500 hours, a clock frequency of 0.2 Hz, an adjustment angle of 45°, a coefficient of friction of 0.28, a journal diameter of 4.7 mm, a pressure pulsation of more than 200 mbar, and an exhaust gas pressure of more than 1.5 bar, in the case of a diesel exhaust gas as the test medium.

The material planeness of the adjustable blade according to the invention amounts to less than 0.1 mm, in the case of a circumference with the diameter of 80 mm, during a thermal shock cycle test with a test time of 300 hours.

The material of the adjustable blade according to the invention can be welded by means of conventional welding methods, such as WIG, plasma and also EB methods.

The subclaims contain advantageous developments of the invention.

In one embodiment, the adjustable blade is distinguished by a specific composition which contains the components C: 0.1 to 2%, by weight, Cr: 18 to 43% by weight, Ni: 5 to 15% by weight, Mn: 8 to 16%, by weight, Si: ≦1.3% by weight, Nb: 0.5 to 4% by weight, N: 0.1 to 3% by weight, V: 0.2 to 2.0% by weight, and Fe.

The influence of the individual elements on an iron-based alloy is known, but it was then found, surprisingly, that exactly the composition described produces a material which, when processed into an adjustable blade, has a particularly balanced property profile. As a result of this composition according to the invention, an adjustable blade with particularly high heat resistance and temperature resistance, even up to 900° C., is obtained, which is distinguished by very good sliding properties and therefore low sliding wear or wear due to attrition. Moreover, the erosion resistance is increased, as compared with known materials, and this also applies, furthermore, to wet corrosion. The material and therefore the adjustable blade according to the invention, moreover, are extremely dimensionally stable, and the material therefore has high strength and deformation resistance.

These properties can be improved even further. For this purpose, according to one embodiment, the adjustable blade according to the invention consists of a material which contains the following elements: C: 0.2 to 1.0% by weight, Cr: 20 to 32% by weight, Ni: 7 to 14% by weight, Mn: 9 to 14.5% by weight, Si: ≦1% by weight, Nb: 0.75 to 3.5% by weight, N: 0.1 to 1.0% by weight, V: 0.3 to 1.6% by weight, and Fe.

An adjustable blade produced in this way not only has the high heat resistance of up to 900° C., but also markedly improved sliding properties. The sliding wear is minimized here. Moreover, resistance to corrosion and erosion is maximized. These properties accompany the very good deformation resistance and dimensional stability of the adjustable blade according to the invention at high temperatures.

A material produced in this way and therefore the adjustable blade according to the invention thus have the following properties:

Mechanical properties Value Measurement methods Tensile strength R_(m) >685 MPa ASTM E 8M/EN 10002-1; at increased temperature: EN 10002-5 Yield point R_(p0.2) >330 MPa Standard method Elongation at break >14% Standard method Hardness 205 to 265 HB ASTM E 92/ISO 6507-1 Coefficient of linear 16 to 19 K⁻¹ Standard method expansion (20 to 900° C.)

According to a further embodiment of the invention, the adjustable blade according to the invention or the material forming it, the iron-based alloy, is free of sigma phases. Sigma phases are brittle, intermetallic phases of high hardness. They arise when a body-centered cubic metal and a face-centered cubic metal, the atomic radii of which are identical with only a slight deviation, meet one another. Such sigma phases are undesirable because of their embrittling action and also on account of the property of the matrix to extract chrome. According to this further advantageous embodiment, therefore, the material according to the invention is distinguished in that it is free of sigma phases. This counteracts the embrittlement of the material and increases its durability. The reduction or avoidance of sigma phases is achieved in that the silicon content in the alloy material is lowered to less than 1.3% by weight and preferably to less than 1% by weight. Furthermore, it is advantageous here to employ austenite formers, such as, for example, manganese, nitrogen and nickel, if appropriate in combination.

Claim 5 defines, as an independently handleable article, an exhaust gas turbocharger which, as already described, comprises an adjustable blade which consists of an austenitic basic structure and which has or contains dendritic carbide precipitations.

FIG. 1 shows a perspective view, illustrated partially in section, of an exhaust gas turbocharger according to the invention. FIG. 1 illustrates the turbocharger 1 according to the invention which has a turbine casing 2 and a compressor casing 3 connected thereto via a bearing casing 28. The casings 2, 3 and 28 are arranged along an axis of rotation R. The turbine casing is shown partially in section, in order to make clear the arrangement of a blade bearing ring 6 and a radially outer guide blade cascade 18 which is formed by the latter and which has a plurality of adjustable blades 7 distributed over the circumference and having rotary axes 8. Nozzle cross sections are thereby formed, which are larger or smaller, depending on the position of the adjustable blades 7, and which act upon the turbine rotor 4, located in the center on the axis of rotation R, to a greater or lesser extent with the engine exhaust gas supplied via a supply duct 9 and discharged via a central connection piece 10, in order via the turbine rotor 4 to drive a compressor rotor 17 seated on the same shaft.

In order to control the movements or the position of the adjustable blades 7, an actuating device 11 is provided. This may per se be of any desired design, but a preferred embodiment has a control casing 12 which controls the control movement of a tappet member 14 fastened to it, in order to convert the movement of said tappet member on an adjustment ring 5, located behind the blade bearing ring 6, into a slight rotational movement of said adjustment ring. Between the blade bearing ring 6 and an annular part 15 of the turbine casing 2, a free space 13 for the adjustable blades 7 is formed. So that this free space 13 can be safeguarded, the blade bearing ring 6 has spacers 16.

EXAMPLE

An alloy, from which the adjustable blades according to the invention were formed, was produced from the following elements according to a customary method. The chemical analysis gave the following values for the elements: C: 0.2 to 0.5% by weight; Cr: 23 to 26.5% by weight; Ni: 9 to 13.5% by weight; Mn: 9 to 12.5% by weight; Si: max. 1.3% by weight; Nb: 0.75 to 1.75% by weight; V: 0.7 to 1.6% by weight; N: 0.1 to 0.4% by weight, the rest: iron.

The adjustable blades produced according to this example were distinguished by a tensile strength R_(m) of 687 MPa (ASTM E 8M/EN 10002-1; at increased temperature: EN 10002-5). The yield point R_(p) 0.2 (measured according to standard methods) amounted to 337 MPa. The elongation at break of the material (measured according to standard methods) amounted to 14.2%. The hardness of the material (measured according to ASTM E 92/ISO 6507-1) amounted to 258 HE. The coefficient of linear expansion (measured according to standard methods) amounted to 17.8 K⁻¹ (20 to 900° C.) The material was subjected to a validation test series which comprised the following tests:

-   -   outdoor exposure test     -   changing climate test     -   thermal shock test/cycle test—300 h     -   hot gas corrosion test in a fission furnace

The component was distinguished in all the tests by excellent resistance to the acting forces. The material therefore had extremely high wear resistance and outstanding oxidation resistance, so that corrosion and wear of the material under the specified conditions were markedly reduced, and, consequently, the resistance of the material was still ensured even over a long period of time.

Thermal Cycle Test:

The component according to the invention was subjected to a thermal cycle test, the thermal shocks being operated as follows:

1. use of stationary rotors; 2. 2-turbocharger operation; 3. test duration: 350 h (approximately 2000 cycles); 4. during the entire test, the exhaust gas flap in the turbochargers remains open at 15° C.; 5. high temperature: nominal power point T3=750° C., turbocharger mass flow on the turbine side: 0.5 kg/s; 6. low temperature: T3=100° C., turbocharger mass flow on the turbine side: 0.5 kg/s; 7. cycle duration: 2×5 min. (10 min.); 8. execution of three intermediate crack tests.

LIST OF REFERENCE SYMBOLS

-   1 Turbocharger -   2 Turbine casing -   3 Compressor casing -   4 Turbine rotor -   5 Adjustment ring -   6 Blade bearing ring -   7 Adjustable blades -   8 Rotary axes -   9 Supply duct -   10 Axial connection piece -   11 Actuating device -   12 Control casing -   13 Free space for adjustable blades 7 -   14 Tappet member -   15 Annular part of the turbine casing 2 -   16 Spacer/spacing boss -   17 Compressor rotor -   18 Guide blade cascade -   28 Bearing casing -   R Axis of rotation 

1. An adjustable blade for turbocharger application, particularly in diesel engines, consisting of an iron-based alloy with an austenitic basic structure and dendritic carbide precipitations.
 2. The adjustable blade as claimed in claim 1, which contains the following components: C: 0.1 to 2% by weight, Cr: 18 to 43% by weight, Ni: 5 to 15% by weight, Mn: 8 to 16% by weight, Si: ≦1.3% by weight, Nb: 0.5 to 4% by weight, N: 0.1 to 3% by weight, V: 0.2 to 2.0% by weight, and Fe.
 3. The adjustable blade as claimed in claim 1, which contains the following components: C: 0.2 to 1.0% by weight, Cr: 20 to 32% by weight; Ni: 7 to 14% by weight, Mn: 9 to 14.5% by weight, Si: ≦1% by weight, Nb: 0.75 to 3.5% by weight, N: 0.1 to 1.0% by weight, V: 0.3 to 1.6% by weight, and Fe.
 4. The adjustable blade as claimed in claim 1, wherein the iron-based alloy is free of sigma phases.
 5. An exhaust gas turbocharger, particularly for diesel engines, comprising an adjustable blade consisting of an iron-based alloy with an austenitic basic structure and dendritic carbide precipitations.
 6. The exhaust gas turbocharger as claimed in claim 5, wherein the adjustable blade contains the following components: C: 0.1 to 2% by weight, Cr: 18 to 43% by weight, Ni: 5 to 15%, by weight, Mn: 8 to 16% by weight, Si ≦1.3% by weight, Nb: 0.5 to 4% by weight, N: 0.1 to 3% by weight, V: 0.2 to 2.0% by weight, and Fe.
 7. The exhaust gas turbocharger as claimed in claim 5, wherein the adjustable blade contains essentially the following components: C: 0.2 to 1.0% by weight, Cr: 20 to 32% by weight, Ni: 7 to 14% by weight, Mn: 9 to 14.5% by weight, Si: ≦1% by weight, Nb: 0.75 to 3.5% by weight, N: 0.1 to 1.0% by weight, V: 0.3 to 1.6% by weight, and Fe.
 8. The exhaust gas turbocharger as claimed in claim 5, wherein the material of the adjustable blade is free of sigma phases. 